Math is your “mortal enemy” or “you are not good at it”…
We will start from zero and progress slowly
There is plenty of help available
As long as you put in the time to do the work every week, you will do great!
You don’t think you will be able to “memorize” all the equations …
You really shouldn’t have to memorize anything in this class
Plan for Today
Become familiar with R and RStudio
Become familiar with R
Do calculations: +, -, \(*\), /
Create objects: \(<-\), ”
Use functions: (), sqrt(), #
R and RStudio
Recall, before class today you should have installed two programs in your computer:
R () and RStudio ()
R is the statistical program that will perform calculations and create graphics for us (it’s the engine)
RStudio is the user-friendly interface that we will use to communicate with R
We will never open R directly; we will always start by opening RStudio
RStudio will open R by itself
RStudio
Go ahead and open RStudio ()
Then, open a new R script:
drop down menu: File > New File > R Script
What is a R script?
type of file we use to store the code we write to analyze data
RStudio Layout
RStudio Layout
R Script (upper left window):
Where we write and execute code
R Console (lower left window):
where R provides the executed code and its outputs (including errors)
Environment (upper right window):
Storage room of current R session
Lists objects that we have created
Help and Plots tabs (lower right window)
The R Programming Language
To use R, we need to learn its language
the R programming language
R is both the name of the program and the name of the language
Learning a programming language is like learning a foreign language
not easy
requires practice
requires patience
We will use R to:
Do calculations
Create objects
Use functions
Calculations
We can use R as a fancy calculator
R understands arithmetic operators such as +, -, \(*\), /
Let’s ask R to calculate 20 plus 5
First we type on the R script (upper left window): 20 + 5
Then, to execute this code: we highlight it and either
Manually hit the run icon ()
Use the shortcut command + enter in Mac or ctrl + enter in Windows
Go ahead and do it
In the console, you should see the following:
20+5
[1] 25
First, the executed code 20 + 5
Then, the output of the executed code ## [1] 25
What does the [1] mean?
It indicates that the output immediately to its right is the first (and only, in this case) output
The title of the R script is now highlighted in a different color to indicate that you have unsaved changes
To save the R script either use shortcuts (command + S or ctr + S) or click on File > Save (or Save As…)
Name it “lecture2” so that you know what it refers to
In our textbooks, as well as in our lectures, you will probably see the output that you should see in the console right after the code that produces it, like so:
20 + 5
## [1] 25
20 + 5 is the code to be typed and executed on the R script (the code that R will execute)
The symbol ## indicates the beginning of the output
[1] 25 is the output (what you should see in the console after the executed code)
Create Objects
R Stores information in the form of objects
In order to analyze data, we will need to create objects
An object is like a box that can contain anything
To create an object, we need to:
Give it name
Specify its contents
Use the assignment operator \(<-\)
In R, we use the assignment operator \(<-\) to create an object:
To its left, we specify the name of the object
A name cannot begin with a number, contain spaces, or special symbols (i.e., $ or %) that are reserved for other purposes
A name can contain _ underscores, which are good substitutes for spaces
To its right, we specify the content of the object
object_name \(<-\) object_content
object_name \(<-\) object_content
For example, type and run:
object_name twentyfive \(<-\) 25 object_content
After executing this code, the object twentyfive will show up in the Environment (the upper right window of RStudio)
To find out the contents of an object, you can run the name of the object in R:
twentyfive <-25twentyfive
[1] 25
Objects can contain text as well as numbers
Execute: class \(<-\) “pols2972Q”
Now in the environment there should be two objects
What are they?
Note that in this last piece of code we used ” around the contents, but we did not use ” in the previous piece of code
twentyfive \(<-\) 25 vs class \(<-\) “pols2972Q”
Why?
When do we need to use ” when writing code in R?
the names of objects, names of functions, and names of arguments as well as special values such as TRUE, FALSE, NA, and NULL should NOT be in quotes
All other text should be in quotes
Numbers should never be in quotes unless you want R to treat them as text
What would happen if you executed: class \(<-\) pols2972Q
You will receive an error: Error: object ’pols2972Q not found
without the ”, R thinks that pols2972Q is the name of an object and R is right; there is no object called pols2972Q in the environment
Running into errors is part of the coding process
Do not be discouraged
If you have problems figuring out what a particular error means, Google it; there are lots of Q&A sites
Copy and paste the error directly into Google
R will overwrite objects if you assign new content to an existing object name
class <-"pols2972Q"class
[1] "pols2972Q"
class <-"data analysis"class
[1] "data analysis"
Notice that class now contains the text “data analysis” instead of “pols2972Q”
R is case sensitive
class is different than Class
To avoid confusion, try to utilize lower-case letters when naming objects
Use Functions
Think of a function as an action that you request R to perform on a particular object or piece of data, such as calculating the square root of 25
A function:
takes input(s)
example: takes the number 25
Performs an action with the input(s)
computes \(\sqrt{25}\)
Produces an output
Produces the number 5
We will learn how to use these functions and others throughout this semester:
) and RStudio (
)
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